Rotary mill

ABSTRACT

A ROTARY MILL FOR FINE COMMINUTION WITH THE AID OF GRINDING BODIES COMPRISES A ROTARY SHELL HAVING A SUBSTANTIALLY CONICAL INNER SURFACE IN DIAMETER IN GOING FROM BOTTOM TO TOP AND WHICH IS ADAPTED TO ROTATE ABOUT A CENTRAL VERTICAL AXIS OF THE ROTARY SHELL, AND AT LEAST ONE GUIDE PLATE IS ARRANGED IN THE UPPER PORTION OF THE INTERIOR OF THE ROTARY SHELL FOR DIRECTING GRINDING BODIES DOWNWARDLY AFTER THEY ARE MOVED UPWARDLY ALONG THE SUBSTANTIALLY CONICAL INNER SURFACE IN SPIRAL PATHS BY CENTRIFUGAL FORCES.

ROTARY MILL 4 Sheets-Sheet 1 Filed March 6, 1969 FIG,

INVENTOR TA rsuo HAG-l WA 24 KARL RAT ATTORNEY 1971 TATSUO HAGIWARA 3,615,051

ROTARY MILL Filed March 6, 1969 4 Sheets-Shoot ;3

FIG: 2

e .=r E I5 29 24 8A 8A 26 3 Q; L 25 T61 IE U) 8 l 111 l4 l7 l3 I3 I 22 9 g I2 s |Q ,m I' 4 I II I 'INVENTOR 72: rs uo HA 'r/ WA): 4

BY H mm. 24m

ATTORNEY Oct. 26, 1971 TATSUQ HAGlWARA 3,615,057

ROTARY MILL Filed March 6, 1969 4 Sheets-Sheet 3 INVENT OR 7 754x900 HAG W424 BY ITA 18L, QA TH ATTORNEY Oct. 26, 1971 TATSUO HAGIWARA 3,615,057

ROTARY MILL Filed March 6, 1969 4 Sheets-Sheet 4 FIG, 4

6 29 VFB Y N 33 I 2| 8A 25 22 4 ,A 8J l6 INVENTOR 7747 500 H4CY/WAQ4 BY )rARL RArH ATTORNEY United States Patent M 3,615,057 ROTARY MILL Tatsuo Hagiwara, Tokyo, Japan, assignor to Kawasaki Jnkogyo Kabushilti Kaisha, Kobe-shi, Japan Filed Mar. 6, 1969, Ser. No. 804,854 Claims priority, application Japan, Mar. 12, 1968, 43/ 15,566 Int. Cl. 1302c 17/04, 17/10 US. Cl. 241-53 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a rotary mill for fine comminution comprising a rotary shell loaded with a multitude of grinding bodies and a material to be processed, said grinding bodies impinging on one another or rolling on an inner wall of said rotary shell while said rotary shell is being operated whereby particles of the material interposed between the grinding bodies themselves and the grinding bodies and the inner wall of the rotary shell can be ground into fine powder. Conventional rotary mills of the type described are designed so that their cylindrical rotary shell is rotated about a horizontal axis. During rotation of the rotary shell, the grinding bodies contained therein are moved upwardly through substanitally half the circumference of the shell from their lower positions in the shell while grinding the material to be treated on the inner wall of the rotary shell till they reach the uppermost positions in the shell when they drop onto the bottom of the shell to repeat the operation described above. Accordingly, it is only through substantially one half the circumference of the rotary shell that is concerned in the grinding operation, with the remainder being rendered inoperative. With such rotary mills, it is impossible to increase efiiciency in performing a grinding operation by increasing the number of revolutions of the rotary shell, since the material to be processed and the grinding bodies will be brought into intimate contact with the inner wall of the shell, in which there is no relative motion between the inner wall of shell and the grinding bodies, and maintained in said state by centrifugal forces if the number of revolutions of the rotary shell exceeds a given level. Thus, the comminution capacity of a rotary mill per unit volume thereof has hitherto been restricted to a relatively low level. The present invention obviates the aforementioned disadvantage of conventional rotary mills. Accordingly, the invention has as its object the provision of a rotary mill which permits increasing the number of revolutions of the rotary shell as desired and which makes it possible, therefore, for a small size rotary mill to operate at the same efficiency as conventional rotary mills.

According to the present invention, there is provided a rotary mill comprising a rotary shell having a substantially conical inner surface, an inner diameter of which increases in going from bottom to top, said rotary shell being adapted to rotate about a vertical axis extending through the apex of the substantially conical rotary shell, and at least one guide plate is mounted in the upper portion of the substantially conical rotary shell for bringing 3,615,057 Patented Get. 26, 1971 grinding bodies to a stall and/or causing the same to change their directions of movements so that they may be returned to the lower portion of the interior of the shell after they have moved upwardly along said conical inner surface of the shell in spiral paths by centrifugal forces resulting from rotation of the shell.

Other objects and advantages as well as features of the invention will become apparent from the description of embodiments of the invention set forth hereunder when considered in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of a rotary mill embodying the present invention, with certain parts being cut out, in explanation of the principles of this invention;

FIG. 2 is a sectional view of another embodiment of the rotary mill according to this invention;

FIG. 3 is a sectional view taken on the line HI-III of FIG. 2;

FIG. 4 is a sectional view of still another embodiment of the rotary mill according to this invention; and

FIG. 5 is a sectional view taken on the line VV of FIG. 4.

In FIG. 1, a rotary shell generally designated 1 has a substantially conical inner surface 2 which increases in diameter in going from bottom to top. The rotary shell 1 is rotated at high speeds about a vertical center line A of the inner surface by a shaft 4 connected to a bottom plate 3. The conical inner wall 2 is contiguous with a cylindrical wall 5 at the upper end edge of the former. A stationary cover 6 is mounted on the upper edge of the cylindrical wall 5. The rotary shell 1 is loaded with a multitude of grinding bodies or balls 7 and a material to be processed. 8 refers to a plurality of guide plates firmly secured to said stationary cover 6 for guiding the grinding bodies, each of said guide plates being arcuate in form and mounted vertically such that it is curved in the direction of rotation of the shell 1 with one end thereof being disposed in close proximity to said cylindrical wall.

In operation, the rotary shell 1 rotates at high speeds and the grinding bodies or balls 7 disposed on the bottom plate 3 rotate with the rotary shell 1 to be moved out wardly and brought into contact with the lower end of the inner surface 2'by centrifugal forces. The balls are then moved upwardlyalong the inner surface 2 to travel in spiral paths by centrifugal forces. B designates a spiral upward path of travel of one ball 7. Actually, a multitude of balls 7 simultaneously move upwardly along the inner wall in a multitude of spiral paths, and during their upward movements the balls roll on the inner surface 2 and reduce the particles of the material interposed between the balls and the inner surface of the rotary conical shell to finely ground powder. Upon reaching the upper end of the inner surface 2 the balls 7 move along the guide plates 8 till they reach the end of each of the guide plates disposed near the center line A when they are brought to a stall and drop onto the bottom plate 3 of the rotary shell 1. While they move downwardly, the balls impinge on one another and further grind the material coming between them. C designates a path of the downward movement of a ball 7. Upon reaching the bottom plate 3 the balls 7 are again moved and brought into contact with the lower end of the inner surface 2 by centrifugal forces to repeat the operation just described. Each of the guide plates 8 may be twisted such that the end edge thereof which is disposed near the center line A is inclined with respect to the center line A and the inner surface of the arcuate guide plate is increasingly directed downwardly in going toward said end, whereby the balls 7 can be readily directed to move downwardly. Alternatively, the guide plates 8 may be rotatably mounted to move in relative motion with respect to the balls 7 moving on the inner surface 2, instead of being firmly fixed to the stationary cover 6. The number ofthe guide plates is not limited 1 to two as disclosed herein. There may also be provided only one guide plate or more than two guide plates without departing from the spirit or scope of the invention. The guide plate'or plates may be of any shape as desired, so long as the grinding bodies can be advantageously guided toward the center of rotation-of the rotary conical shell.

, In the embodiment shown in'FIGS. 2 and 3, a bearing box is firmly secured to a framework 9. The bearing box 10 mounts therein bearings 11 and 12 for rotatably supporting the vertical shaft 4 which in turn rotatably supports the rotary shell -1. The rotary shell 1 is formed with an annular flange 13 extending horizontally outwardly from the upper end edge 14 of the rotary shell. The tubular cover 6 firmly secured to the upper portion of the framework 9' has an annular plate 15 secured to and extending horizontally outwardly from the lower end of the tubular cover. Depending from the outer edge of said annular plate 15 is a cylindrical wall plate 16 having a lower end which is spaced apart from the upper face of the annular flange 13 by a clearance 17 which is preferably reduced in dimension. The wall plate 16 is formed therein with a number of slots 18 disposed at regular intervals. Each of the guide plates 8 formed with a mounting portion 19 is inserted in each of said slots 18 from outside and firmly attached to the outer surface of wall plate 16 at its mounting portion 19. In addition, the inner end 8A of each guide plate 8 is disposed outwardly with respect to the upper end edge 14 of the inner surface 2. An enclosure 20 is attached to the marginal portion of the annular flange 13 so that the enclosure 20 may extend vertically to thereby form an annular powder chamber 21 between the wall plate 16 and the enclosure 20. A scraper plate 22 "attached to each guide plate 8 projects into said powder chamber 21. 1A powder return passage 23 is formed between the base of the scraper plate 22 and the guide plate 8. The annular plate 15 is formed with a number of air introducing openings 24, and a partition plate 25 depends from'the inner side of each of said air introducing openings24 so as to form an air passage 26 between the partition wall 25 and the wall plate 16. 27 refers to a line for supplying therethrough a material to be processed, and 28 is a duct for discharging finely ground powders and air by suction. In operation, an electric motor (not shown) is actuated to drive the shaft 4 for rotating the substantially cone shaped rotary shell 1. At the same time, a material to be processed is continuously supplied through the material supply line 27 and the material reduced to finely ground powder is discharged by suction through the duct 28. During the operation, the grinding bodies or balls 7 move upwardly along the conical inner surface of the rotary shell in spiral paths while effecting grinding of the material in the same manner as described with reference to the embodiment shown in FIG. 1. Upon reaching the upper end edge 1-4 of the conical inner surface 2 the grinding bodies find their way into a space between the annular flange 13 and the annular plate 15 where they are guided by the guide plates 8 and moved inwardly in their movements and/ or brought to a stall, dropping onto the bottom plate 3 of the'rotary shell 1. The grinding bodies which have fallen on the bottom plate 3 again move upwardly along the conical inner surface 2 to repeat the grinding operation. During this operation, air is introduced through a suction opening 29 formed in the upper portion of the enclosure 20 and led through the air introducing openings 24 and air passages 26 to be drawn by suction and discharged through the duct 28 together with finely ground powder of the material processed. The powder finding its way into the powder chamber 21 through the clearance 17 is scraped by the scraper plate 22 and returned, through the return passages 23, to the portion of the interior of the shell 1 disposed immediately inwardly of the wall plate 16 where the powder is subjected to a downwardly directed air current prevailing in the air passage 26, so that it is moved further inwardly toward the center of the shell 1.

In the embodiment shown in FIGS. 4 and 5, a separator 30 ofcone shape is firmly attached to the underside of the stationary cover 6 such that said separator 30 is arranged about the center line A and in a space formed above the inner surface 2 of the inverted cone portion of the shell 1. The separator 30 is formed at its base with an annular opening 31 which is provided with a number of vanes 32 mounted therein. The direction in which the vanes 32 face is determined such that an air current swirling in the same direction as the rotation of therotary shell 1 can be generated in the separator 30 by the vanes 32. The separator 30 is formed at its lower end with a gross particle outlet port 33. An auxiliary separator 34 is mounted inside the separator 30 for causing an air current introduced through the suction opening 31 to move in a roundabout way. The duct 28 is connected to the separator 30.

In operation, air is introduced into the shell 1 through the suction opening 29 formed in the upper portion of the enclosure 20, the air introducing openings 24 formed in the annularplate 15 and the air passage 26 and caused to swirl by the vanes 32 together with finelyground powder of the material and driven into the separator 30 through the suction opening 31. The air together with finely ground powders is discharged through the duct 28 out of the separator 30. While passing through the separator, gross particles of the material are separated from finely ground powder in accordance with the principles of a cyclone and drop through the gross particle outlet port 33 into the interior of the shell 1.

It is to be understood that although the inner surface of the rotary shell 1 has been described as being substantially conical in shape, the inner surface is not limited to this shape. The inner surface may, for example, be either convexed or concaved without departing .from the spirit and scope of the invention. In short, the inner surface of all shapes which permit the grinding bodies to readily effect upward movements along the inner surface in spiral paths by virtue of centrifugal forces are covered by this invention.

It is also to be understood that the grinding bodies used for carrying the present invention into practice are made of a wear resisting material but need not necessarily be of the ball shape, and that cylindrical grinding bodies used in milling cement may also be used in the present invention. A notable advantage of the rotary mill according to the present invention over conventional rotary mills lies in the fact that the inner surface 2 of the rotary shell 1 can be fully utilized in performing a grinding operation since the grinding bodies are scattered throughout the entire surface of the substantially conical inner surface 2 of the rotary shell 1. In addition, when the speed of rotation of the rotary shell 1 is increased, the grinding capacity of the mill can positively be increased because the grinding bodies and the material to be processed are not brought into intimate contact with the inner surface 2 but move upwardly along the inner surface in spiral paths at all times and return to the bottom of the rotary shell by at least one guide plate. Another advantages of the rotary mill according to the present invention lies in the fact that the arrangement, in which at least one guide plate is mounted above the annular horizontally outwardly extending flange 13 of the shell so that the inner end of the guide plate may be disposed outwardly of the outer end edge of the inner surface of the rotary shell, can prevent the grinding bodies from violently impinging on the underside of the guide plate. This is conductive to prevention of wear of and damage to the grinding bodies and loss of power due to the violent impinging of the grinding bodies on the underside of the guide plate.

The arranging of a separator (as in FIG. 4) of the substantially conical shape in a space defined by the stationary cover in the upper portion of the rotary shell above the inner surface thereof and the provision of a number of vanes in an annular air suction opening formed in the base of such separator for causing an air current to swirl in the same direction as the rotary shell makes it possible to separate finely ground powder from gross particles based on the principles of a cyclone. This permits the production of finely ground powder of good quality and also the return of the gross particles to the interior of the rotary shell for further processing.

From the foregoing description, it will be appreciated that the present invention permits one to increase the grinding capacity of a rotary mill by increasing the number of revolutions of the mill and also to increase efiiciency per unit volume of the mill because the inner surface of the mill can be fully utilized in eifecting a grinding operation. The invention also makes possible an overall small size in a rotary mill and a reduction in the consumption of power.

I claim:

1. A rotary mill of the type comprising a rotary shell loaded with a multiplicity of grinding bodies, which shell is adapted to receive a material to be finely ground, means for mounting said shell for rotation about a vertical axis, said shell having a first portion with a substantially conical inner surface increasing in diameter from the bottom to the top thereof and a substantially cylindrical enclosing wall extending upwardly from the top of the first portion, at least one guide plate constructed to receive those grinding bodies which pass the conical inner surface of the shell to redirect the grinding bodies toward the central area of the shell so that they may return to the lower part of the rotary shell, and stationary means for holding said guide plate above, but adjacent to, the plane of the top surface of the conical portion.

2. A rotary mill as defined in claim 1, wherein said shell comprises an outwardly flanged portion connecting the conical portion of said shell to the cylindrical enclosing wall thereof, said guide plate being positioned above and adjacent to said flanged position and within said enclosing wall, in such a manner that the inner end thereof is disposed outwardly of the upper edge of the substantially conical inner surface.

3. A rotary mill as defined in claim 1 wherein the stationary means for holding said guide plate is a cover.

4. A rotary mill as defined in claim 2, wherein the stationary means for holding the guide plate is a cover, meansaextending through the cover for introducing material-to-be-ground into the rotary shell, said cylindrical enclosing wall and cover being constructed to permit air to flow into the space Within said enclosing wall, and a duct connected to the stationary cover for discharging finely ground powders of the ground material by suction.

'5. A rotary mill as claimed in claim 4 wherein said cover includes a cylindrical wall connected to the outer margins of said cover, but concentric with and within the cylindrical enclosing wall of said shell, and means for returning powder collecting in the space between the cylindrical enclosing wall of said shell and the cylindrical wall of said cover to within the latter.

6. The rotary mill as claimed in claim 2, comprising a separator of substantially conical shape firmly attached to the underside of the stationary cover and arranged about the vertical center line of the rotary shell in the upper portion of the interior of the rotary shell, said separator being formed at its base with an annular opening for introducing air current into the separator and provided with a number of vanes mounted in said annular opening forcausing air currents to swirl in the direction of rotation of the rotary shell, said separator being maintained in communication with said duct for discharging finely ground powder of said material by suction.

7. The rotary mill as claimed in claim 6, wherein said separator is positioned above the substantially conical inner surface of said shell and wherein said separator comprises a gross particle discharge port formed on the underside thereof for returning gross particles of the material to the lower portion of the interior of the shell.

References Cited UNITED STATES PATENTS 1,479,242 1/1924 Johnson 241-176X DONALD G. KELLY, Primary Examiner US. Cl. X.R. 

